Status (by robm at Thu Mar 5 08:01 UTC)
Due to some co-ordinated fraudulent signups, a number of emails that were spam were sent via FastMail systems. This caused Hotmail to block FastMail’s servers between about 01:15 and 02:20 EST.
We’ve now locked the offending accounts, put some blocks in place to try and stop this happening again, and switched IPs so that emails are now going through to Hotmail correctly.